Science

• Digestion


  Process by which food is broken down into smaller components
• Types of digestion

  • Mechanical (physical)
  • Chemical
• Mechanical digestion


  • Chew
  • Tear
  • Grind
  • Mash
  • Mix
• Chemical digestion


  • Enzymatic reaction to improve digestion of carbohydrates, protein, lipids
• Phases of digestion


  • Ingestion
  • Mechanical digestion
  • Deglutition
  • Chemical digestion
  • Absorption
  • Elimination/Excretion
• Mastication


  Food is cut and chewed into smaller pieces with the use of our teeth
• Bolus


  Lubricated food (ball shaped) mass of food
• Enzymes


  • Carbohydrases (for carbohydrates)
  • Proteases (for proteins)
  • Lipase (for lipids)
• Parts of the digestive system


  • Mouth/Buccal cavity
  • Pharynx
  • Esophagus
  • Stomach
  • Small Intestine
  • Large Intestine
• Teeth


  • Break down food into smaller pieces; 32 teeth
  • Incisors (8 front teeth that bite, cut, slice daily food)
  • Canine (4 sharpest teeth for tearing apart food)
  • Premolars (8) and molars (12) near the back for tearing and crushing food
• Tongue


  Mixes food with saliva (contains amylase which helps break down starch; amylase aka ptyalin)
• Epiglottis


  Flap-like structure at the back of the throat that closes over the trachea preventing food from entering it
• Esophagus


  20 cm long; secretes mucus; peristalsis (moves food from throat to stomach using muscle movement)
• Heartburn


  When acid from the stomach gets in the esophagus
• Cardiac sphincter


  At the end of the esophagus
• Stomach


  • J-shaped muscular bag that stores the food you eat, mixes food with digestive juices, and breaks down protein and lipids
  • Digestive juices: Hydrochloric acid (HCl) kills bacteria, Pepsinogen - an enzyme that digests protein
  • Chyme - food found in stomach
• Small Intestine


  • 6 meters long, 2.5 cm diameter; longest organ
  • Divisions: Duodenum (25 cm), Jejunum (1.4 m), Ileum (3.5 m)
  • Villi - lining of intestine wall
  • Microvilli - covers villi
• Large Intestine


  • 1.5 meters long, 5 cm diameter; accepts what small intestine doesn't absorb
  • Functions: Absorbs vitamins (bacterial digestion), reabsorbs water, concentrates waste and stores feces
  • Parts: Ascending colon, Transverse colon, Descending colon (appendix)
• Defecation


  The feces comes out of the anus
• Accessory organs of digestion


  • Liver
  • Gall bladder
  • Pancreas
  • Salivary glands
• Liver


  • Directly affects digestion by producing bile, filters out toxins and waste including drug, alcohol and poison
• Gall bladder


  • Stores bile; releases it into the small intestine
  • Gallstones - from fatty diets
• Pancreas


  • Produces digestive enzymes to digest fats, carbohydrates and proteins
  • Produces insulin
• Salivary glands


  • Facilitate mastication, swallowing, and speech
  • Types: Parotid, Submandibular, Sublingual
  • Provide an aqueous medium for taste, participate in the digestion of triglycerides and starches
• Enzyme


  Protein that speeds up a chemical reaction without being destroyed; organic catalyst
• Enzymes


  • Affected by temperature (30°C-40°C) and pH of the substrate
  • Take too long to complete reactions on their own
  • Catalytic proteins that change the rate of reaction without being consumed
  • Active site - pocket/groove on enzyme that binds to substrate
• Carbohydrate digestion


  • Monomers (small molecules that can be linked to make larger molecules)
  • Monosaccharides (glucose, fructose, galactose)
  • Disaccharides (maltose, sucrose, lactose)
  • Polysaccharides (starch)
• Carbohydrate digestion


  1. Mouth: Carbohydrate + ptyalin → Disaccharide

  2. Stomach: Bolus (disaccharide) changed into chyme

  3. Small intestine: Enzyme amylopsin in pancreatic juice repeats work of ptyalin

  4. Intestinal glands: Release final enzymes for carbohydrate digestion
• Protein digestion


  1. Mouth: Digestion is purely mechanical

  2. Stomach: Protein + pepsin → small polypeptides

  3. Small intestine: Protein + trypsin → polypeptides + dipeptides

  4. Intestinal glands: Polypeptides + aminopeptidases → amino acids, Dipeptides + erepsin (dipeptidase) → amino acids
• Fat (lipid) digestion


  1. Small intestine: Nucleic acid-rich food + nuclease → nucleotide

  2. Intestinal gland: Nucleotide + nucleotidase → Nucleoside + phosphoric acid, Nucleoside + nucleotidase → pentose + nitrogenous base
• Digestive system disorders


  • Indigestion/dyspepsia
  • Constipation
  • Diarrhea
  • Heartburn
  • Ulcer
  • Flatulence
  • Colitis
• Indigestion/dyspepsia


  Food stagnation, over-reacting, eating too fast; symptoms include feeling of fullness, bloating, pain in upper abdomen, nausea, vomiting, abnormal distension
• Constipation


  Dry fecal material or stool, caused by stress and some medications; can lead to colon cancer and multiple sclerosis
• Diarrhea


  Loose, watery, frequent bowel movements when feces pass along colon too rapidly; caused by infection, poor diet, nervousness, toxic substances, irritants in food
• Heartburn


  Acid reflux syndrome, Gastro-esophageal reflux disease (GERD); small quantities of stomach acid are regurgitated into the esophagus, causing a burning sensation
• Ulcer


  Sore or lesion that forms in the mucosal lining of the stomach or duodenum; primary cause is H. pylori bacteria, lifestyle factors include alcohol, stress, certain drugs; symptoms include burning pain in abdomen
• Flatulence


  Excessive amount of gases stored in the digestive system
• Colitis


  Inflammation of the large intestine or colon; symptoms include bloody mucus in the stool, weight loss, urgent bowel movements, tiredness, nausea
• Cell is the basic unit of structure and function of life
• Types of cells


  • Prokaryotic (one-celled organism)
  • Eukaryotic (contains organelles surrounded by membranes)